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Grain weight (GW) is the important basis for predicting the field production,and the development of grain weight related molecular markers could be used for high-yield wheat breeding.Here, we found a new gene, TaGW-3B, associated with wheat kernel weight by the method of screening EST sequences and EST-based molecular assembly and cloning.TaGW-3B was located on chromosome 3BL, closely linked to the SSR marker Xwmc418 in the recombinant inbred line (RIL)population derived from the cross jing411 (J411) × hongmangchun21 (HMC21).In this study, we also developed a complementary co-dominant marker and a dominant marker based on the sequence variation from TaGW-3B.The complementary co-dominant marker could explain from 8.5% to 21.3% phenotypic variations in the RIL population.A recombinant inbred line (RIL) population, one natural population and 273 Chinese wheat micro-core collections were used for marker-trait correlation analysis.Two alleles of TaGW-3B, which were denoted by A-type and B-type respectively, were identified in those accessions.All the differences in average thousand grain weight (TGW) were significant.Marker-trait correlation analysis indicated that the TGW of lines carrying A-type allele was significantly higher than the lines carrying B-type allele (P<0.01).A-type allele was considered a superior allele and significantly associated with grain weight.Moreover, only 60 A-type alleles (including 23 landraces and 37 release cultivars) of TaGW-3B were detected in 385 wheat cultivars (121 landraces and 264 release cultivars), and 42 A-type alleles were detected in 273 Chinese wheat micro-core collections.The result showed that the excellent allele was rarely selected in the previous breeding.By comparing the sequences of TaGW-3B between higher-grain-weight variety and lower-grain-weight variety, five bases insertion in coding region of TaGW-3B was found in the higher-grain-weight variety.The insertion mutation could result in a downstream frame-shift mutation and premature termination of the predicted protein.All the results suggested that TaGW-3B may negatively regulate grain weight.In a word, the successful development of gene markers related to grain weight provides a useful tool for improving grain yield in wheat breeding.